Field of the Invention
The present invention relates to an image capturing apparatus such as a single-lens reflex camera, and a converter device that is attached between an interchangeable lens, which is attachable to and detachable from the image capturing apparatus, and the image capturing apparatus.
Description of the Related Art
In the field of image capturing systems including image capturing apparatuses (e.g., single-lens reflex cameras or mirrorless cameras) and interchangeable lenses that are attachable to and detachable from the image capturing apparatuses, converter devices that are attached between an image capturing apparatus and an interchangeable lens are known. Such image capturing systems expand imaging functions and increases imaging magnifications by using the converter devices. Japanese Patent Application Laid-Open No. 2015-102734 discusses a teleconverter for extending the focal length of an interchangeable lens.
In the teleconverter discussed in Japanese Patent Application Laid-Open No. 2015-102734, a lens component having negative refractive power and a lens component having positive refractive power are arranged in order from the object side. The focal length of the interchangeable lens is extended by making axial light flux be afocal with the lens component having negative refractive power and by converging the light flux with the lens component having positive refractive power. The teleconverter is directed to extending the focal length while keeping optical performance, by arranging the lens component having negative refractive power at a position where the height of an axial ray becomes high.
The teleconverter discussed in Japanese Patent Application Laid-Open No. 2015-102734 is arranged on the image side of an imaging lens that has a long focal length and has a relatively long back focus. When the teleconverter is attached to the imaging lens having a long back focus, the teleconverter can be arranged on the object side comparatively, which makes it possible to arrange the lens component having negative refractive power at a position where the height of an axial ray becomes high. As a result, the focal length of the imaging lens can be readily extended.
On the other hand, when the teleconverter is attached to an imaging lens having a relatively short back focus, the attachment position of the teleconverter is moved toward the image side, as compared with the case where the teleconverter is attached to the imaging lens having a long back focus. In this case, the lens component having negative refractive power is arranged at a position where the height of an axial ray is low, which makes it difficult to sufficiently extend the focal length of the imaging lens.
The back focus typically tends to be short in interchangeable lenses having wide field angles, so that it is often difficult to extend the focal lengths of those interchangeable lenses by attaching converter device between such an interchangeable lens and a camera body.
Further, mirrorless cameras have no quick return mirrors, so that the back focus to be required is shorter as compared with single-lens reflex cameras. Consequently, interchangeable lenses for mirrorless cameras can be readily downsized as compared with interchangeable lenses for single-lens cameras. Meanwhile, from the viewpoint of space, in the interchangeable lenses for mirrorless cameras, it is often difficult to extend the focal length of those interchangeable lenses by attaching a converter device.
As such, conventional converter devices are unsuitable for the interchangeable lenses having relatively wide field angles or the interchangeable lenses for mirrorless cameras. In addition, the conventional converter devices have difficulty sufficiently extending the focal lengths of those interchangeable lenses.